1. Field of the Invention
This invention relates to the field of projectile guidance apparatus, and in particular to an inexpensive conveniently-added-on supplemental guidance module which can be interspersed between the warhead and the motor or like body of a projectile such as a rocket, being activated by forces produced during propulsion, and operative by actuating peripheral incremental explosive charges to damp deviations from a nominal one gravity flight path.
2. Prior Art
A variety of means are known in the prior art for controlling the flight of a projectile weapon subsequent to launch. Such means may include very-sophisticated inertial guidance mechanisms capable of accurately monitoring acceleration of the projectile weapon and thereby keeping track of the location of the projectile even after a flight of many miles The present invention, however, is concerned with a low-cost supplemental guidance system that can be employed at minimal expense in connection with standard forms of direct fire rockets and other projectiles in general purpose use, and will incrementally improve the accuracy thereof. Many projectiles include a body and a payload, with means for propelling the body and payload toward a target. The payload may be a nose-mounted explosive charge, or the nose may contain a fuse for igniting an explosive charge in the body. Typically the nose is threaded to the body. Where the projectile weapon is a rocket, the body of the rocket includes the rocket motor and propellant supply for driving the rocket forward. The explosive charge, warhead or other payload is functionally independent of the body and is located in a nose section which is threaded to the rocket body. A rocket of this type in the U.S. arsenal is the Mark 66, mod. 0 or mod. 1. The rocket has a plurality of arcuate tail fins which spring out upon launch, from a stowed location flat against the cylindrical rocket body, whereupon the fins impart a stabilizing spin to the rocket during flight. The fins are arranged such that during the flight the direction of spin changes. The propellant burn produces a spin which the fins cancel and then reverse after the fuel propelling the rocket is exhausted. The Mark 66 rocket body can be deployed with a number of different warheads. These include, for example, practice inert warheads, explosive charges, armor piercing charges, incendiary white phosphorous charges, aerial flares or anti-personnel charges such as fragmentation devices and/or flechettes. Accordingly, based upon tactical needs, the user can deploy whichever of the rocket warheads needed to produce the desired effects and thus adapt the available ordnance to the requirements of the situation.
The prior art includes a variety of different guided missiles, for example remotely-guided missiles that are attached to a controller at the point of launch by means of thin wires which unspool during flight, self-guided missiles which seek a point of infrared radiation or which home on the reflection of a laser. A typical inexpensive barrage rocket, however, is simply aimed and fired, being a direct fire device with no means provided to monitor the accuracy of flight. During launch or after launch, however, a number of disruptions can occur which may cause the rocket to diverge from the nominal path from the point of launch to the target. With certain types of payloads, the accuracy of the rocket is of less concern than with other types. For example, a smoke payload or an anti-personnel fragmentation payload need only generally hit the target. An armor-piercing round, however, must be quite accurate in order to successfully pierce defensive armor. While it might be possible to equip all the rocket bodies with supplemental guidance systems in the rocket body, thereby achieving the accuracy and/or range needed for accuracy-sensitive payloads such as armor piercing charges this would not be cost effective, and may be counterproductive. The accuracy of the rocket or its cost would be unnecessarily increased for some uses. Given the compromises often made and the design trade offs involved in a rocket design, the designed accuracy would probably be only marginally adequate in accuracy-sensitive situations. Therefore, there is a need to provide a supplemental guidance system for a rocket body which is optional. The supplemental module should be adequate for accuracy-sensitive charges, self-contained, and having no electrical connections and drawing no power, control or sensory input from the payload or the rocket body.
Such a supplemental guidance apparatus would be useful not only in rockets, but also in other forms of projectiles such as artillery and mortar rounds. In connection with the Swedish "STRYX" projectile weapon, a five inch mortar-type shell is lobbed toward a target, the shell including microwave radar means to detect the target and fluid nozzles guiding the projectile on the downstroke, to home on the target. The control is not a self-contained supplemental apparatus. Variations in position of control surfaces are likewise used for guidance, as disclosed in a number of U.S. patents. In U.S. Pat. No. 4,579,298-Thomson, means are provided to axially deflect the nose of a projectile, using solenoid means disposed in the body of a rocket. The device would be inappropriate for use with spin-stabilized devices and has no means for separating the nose section from the body to make the guidance device optional. U.S. Pat. No. 3,141,411-Menke uses a plurality of incremental auxiliary charges to deflect a projectile. The charges are successively deployed at a single reaction motor provided with a detonator and located on the side wall of the projectile weapon. When needed, another of the incremental charges is placed in the side receptacle and detonated when the side receptacle is at the required angular position, being thereby intended to aim the projectile (a rocket) slightly nearer to the target. In this case, the target is detected optically, the rocket being adapted to home on an infrared radiator.
U.S. Pat. No. 4,374,577-Brown et al discloses another form of asymmetrical movable projectile nose. Means are disclosed in this patent to rotate an asymmetrical nose surface as required to deflect the path of the projectile.
U.S. Pat. No. 4,444,119-Caponi teaches a projectile having a plurality of impulse generating explosive charges around the outside, these charges being arranged according to the disclosure to translate the projectile laterally during flight. This apparently requires that the charges be mounted at the same axial position as the center of gravity. In U.S. Pat. No. 3,034,434-Swaim et al, a plurality of such charges are located well forward of the center of gravity of the projectile, such that attitude of the projectile can be corrected as required. The Swaim patent as well as each of the foregoing patents, disclose means designed into each and every rocket of that type, and not a supplemental system which as a wholly self-contained module can correct the attitude of any projectile to which it is attached, and which permits the projectile to operate without using a self-contained supplemental guidance system, if so desired.
In order to guide a projectile with inertial or motion sensors, it is necessary to sense the position of the projectile over time, comparing the position to the expected position, given a nominal flight. With a spin-stabilized projectile, the spin complicates matters, it being necessary to consider the relative orientation of the projectile to vertical In U.S. Pat. No. 4,672,753-Kent et al, a sensor including a toroidal passage with electrical contacts detects the passage of electrolyte fluid for indicating a change in attitude of the sensor. Tilt sensors of this general type are also disclosed in U.S. Pat. No. 4,167,818-Cantarella et al and U.S. Pat. No. 4,628,612-Hori et al. These tilt sensors are normally slow-acting sensors that cannot routinely be employed in a guidance apparatus without some consideration to the fast response time needed. In U.S. Pat. No. 4,628,729-Thoone, the attitude of a vehicle (e.g. an airplane) is sensed using rotational acceleration sensors together with static angle sensors.
Means for detecting the position of a vehicle, such as rocket or other projectile, are also disclosed, for example in U.S. Pat. No. 4,542,870-Howell; U.S. Pat. No. 3,327,631-Howard et al; and U.S. Pat. No. 4,328,938-Reisman et al. In each case the guidance devices are integral with the basic propulsion systems of the rockets or the like, rather than being self-contained add-on modules.
U.S. Pat. No. 4,677,913-Farace and U.S. Pat. No. 4,372,212-Hoelzen et al employ linear or rotational accelerometers such as gyros or the like, in connection with rocket guidance systems (also not of the self-contained type). In these patents, however, the means detecting acceleration linearly (i.e., along the line of flight) or rotationally, also form parts of a safe-and-arming device which disables the control until launch is detected, the sensors thereafter being employed to monitor the position of the projectile.
Notwithstanding all the sophisticated and presumably effective means for guiding projectiles toward a target, there is still a need to incrementally improve the accuracy of inexpensive projectile weapons such as barrage rockets, mortars, ballistic projectiles and similar weapons which may be expended in great numbers. Improvements to the basic propulsion system are not cost effective if each projectile thus requires an expensive guidance system. According to the invention, a supplemental guidance apparatus is provided which is wholly self-contained. Where the projectile to be guided is a rocket having a payload, warhead or fuse device attached on the nose the supplemental device simply is placed between the warhead (or fuse, etc.) and the projectile body, having the required male and female structure as necessary for physically fitting between these parts, but not relying on them for power, sensing or output actuation. On-board batteries, sensors, control means and incremental peripheral thrusters allow for sensing and correction of attitude during the rocket burn, and thereafter. The control means include a programmed processor preferably responsive to inexpensive accelerometer/gyro devices including piezo-electric or fiber optic angular rate sensors for sensing rates of pitch and yaw, and preferably including axial acceleration and roll (spin) sensing devices for detecting launch, and rotation, respectively.
Insofar as the above-mentioned prior art teaches in general the correction of flight path deviations by means of integrating the outputs of accelerometers and the like, their teachings are incorporated by reference. Similarly, the safe-and-arming techniques of these references are also incorporated. The invention improves upon the devices of the references, in the inexpensive and self-contained add-on nature of the supplemental guidance apparatus of the invention which is apt for use with standardized projectile weapons, especially when deployed with accuracy-sensitive warheads, such as armor piercing rounds.